Skin cancer is the most common form of cancer seen in the world. The two most common types of non-melanoma skin cancer include basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). One in five Americans will develop some form of skin cancer at some point in their lives, and it is estimated that over one million Americans will develop skin cancer each year.
Sun exposure has been implicated in the etiology of BCC and SCC. The epidemic rise in the rate of these cancers is directly related to increases in our population's outdoor activities and the desire for a “tanned” skin appearance. Pre-malignant actinic keratoses are common skin growths induced by solar exposure that have the potential for developing into SCC in upwards of 20% of cases. They often appear on the skin years before the development of cutaneous carcinomas.
It is considered a standard of care to remove as many skin cancers and actinic keratoses as possible with the least amount of discomfort, inconvenience and trauma (morbidity), for the patient. Destruction using liquid nitrogen or electrodessication and curettage are effective in removing a majority of skin cancers and actinic keratoses. However, these treatments may not be practical for certain skin cancers located on the face and extremities. Surgical removal of skin cancers and actinic keratoses is not always possible or desirable. Surgery is not practical when many small actinic keratoses are present, and the scarring produced by surgery is generally unacceptable for exposed, relatively visible areas of the skin. Furthermore, it is believed that, in the early stages of their development, many skin cancers and actinic keratoses are so small that it would be difficult or impossible to remove surgically because they are not visible to the eye. Surgery, while necessary for the welfare of the patient, may place the patient at risk and ultimately jeopardize their health if the cancer is located adjacent to certain vital areas, such as the eye. In addition, surgery may lead to a poor cosmetic effect and leave the patient visibly deformed.
Topically applied, chemical agents such as 5-fluorouracil (5-FU, Efudex, Fluoroplex), masoprocol (Actinex), imiquimod (Aldara), and diclofenac (Solaraze) have been approved to eradicate actinic keratoses. While 5-FU has demonstrated efficacy for this purpose, it has been found to cause pain, itching, skin inflammation, ulceration and cosmetic disfigurement often so severe that patients hide at home and stop using it, thus making its therapeutic use unacceptable to many individuals. These effects also preclude the use of 5-FU over large areas of the skin to treat incipient and/or microscopic actinic keratoses. Masoprocol was removed from the US market in 1996 after it was found to have a high incidence of contact sensitivity and allergic reactions. Imiquimod has a relatively good cosmetic effect when treating actinic keratoses but is very expensive for use in large areas of the skin and its packaging in pouches has not been well received by many patients. The Food and Drug Administration recently approved imiquimod for the treatment of BCC. However, this indication excludes treatment of BCC that occurs on the face. Diclofenac is a non-steroidal anti-inflammatory drug (NSAID) used to treat actinic keratoses. It has very modest effects and removal of the actinic keratoses may not be evident until months after treatment ends. However, it causes less irritation than 5-FU and imiquimod and may be useful for some people.
There are several newer therapeutic approaches directed against actinic keratoses that are in clinical trials such as the use of photodynamic therapy (PDT) with aminolevulinic acid. This therapy is a two-step treatment administered over a two-day period. First, the aminolevulinic acid is place over the lesion and on the next day, a blue light is used to activate the drug. However, this treatment is expensive, needs to be done at the doctor's office, is used only for thin lesions, and is not very effective.